Species composition of the biospere


  • Intricate webs of interacting organisms
    • ~2,000,000 species are described
    • ~18,000 plants & animals discovered yearly
    • estimated >85% of species unknown


  • Current composition reflects billions of ways organisms have adapted, over and over, to a changing planet


  • Humans have altered 75% of ice-free surface
    • alters species composition
    • alters livable habitats
    • alters climate

“Essay of the geography of plants” by Humboldt, 1817

Underlying causes of the uneven distribution of plants….

Humboldt’s lessons: Species are spatially arranged

Humboldt lessons: Species are spatially arranged

Similar biological communities reside within our biomes

Climate drives broad distribution of terrestrial biomes

Biomes also have distinct soil types

Species distribution varies widely within biomes

Seasons may impact species distributions

Migration can cross many biomes: Birds

Species may instead be adapted for seasonal habitats

Niche defines the limiting tolerance factors for a species

Ecological Niche =

Tolerance Ranges: Coral Reefs

Ecological niches exist in n-dimensions (many factors)

Distribution of species within biological communities overlap

Fundamental vs Realized Niche =

Species distributions are related to their realized niche space

Species distributions are related to their realized niche space

Species ranges versus distribution: Crocodiles

Species ranges versus distribution: Crocodiles

Ranges versus distribution: Plants more limited by dispersal

dispersal: movement of individuals or gametes
seed dispersal: gravity, wind, water, and by animals

Species ranges versus distribution: Coconut tree

Biogeography and animal ranges: Alfred Wallace 1859

Wallace developed theories of evolution at the same time as Darwin to explain the patterns in biogeography he observed

Zoogeographic regions: Wallace